1) Field of the Invention
The invention relates to spring support assemblies, and more specifically to an improved spring support system for use in chairs, sofas, bedding, car seats, and the like.
2) Description of the Prior Art
Coil spring systems have long been used in seating and bedding to provide a resilient, load-bearing support surface. Such spring systems typically include coil springs variously mounted in a frame or support structure. The springs are supported in the frame or structure by slats, bars, wires, straps, or the like which extend across an open bottom of the frame structure. The coil springs are typically stapled, clipped, crimped, or clinched to the underlying support. Typically, the springs are arranged in rows and columns within the supporting structure. The top ends of the springs are typically interconnected to maintain the spring alignment and spacing, and to assist in distributing applied loads between the springs. The top ends of the springs are often interconnected or xe2x80x9cunitizedxe2x80x9d by a lattice of interwoven straps or by pre-made grids of wire or the like. Alternatively, the tops of the springs may be tied together with a network of twine or wire. Where twine is used, eight-way, hand-tied springs are common, particularly in finer furniture. An example of such eight-way hand-tied springs is illustrated in FIG.6 of U.S. Pat. No. 5,924,682. Though such hand-tied springs provide an effective and comfortable spring support system, the process of hand-tying springs with twine is labor-intensive, and therefore adds significant cost to a spring support system""s production.
One known lower-cost alternative to coil spring suspension systems is a resilient support including so-called xe2x80x9csinuousxe2x80x9d spring assemblies. Sinuous springs are serpentine-shaped lengths of wire. Such a suspension system is described in U.S. Pat. No. 6,116,694. In such an arrangement, sinuous springs are suspended across an open top of a frame. An advantage of such systems is that the springs do not need to be interconnected with each other or otherwise supported in the frame. Unfortunately, such lower-cost systems do not provide the comfort, xe2x80x9cfeel,xe2x80x9d or durability of more costly coil-spring systems.
In another known alternative to coil spring systems, a resilient sheet of stretchable webbing material is tautly stretched across an open support frame without springs. The stretchable material deflects when loads are applied and stretches to conform in shape to an applied load. The material elastically returns to its original shape when loads are removed. Such systems are also much less costly to produce than traditional coil spring systems, but may provide a support surface which is too xe2x80x9cspongyxe2x80x9d, i.e. which lacks adequate stiffness or support.
Therefore, there is a need for an improved spring support system which includes the comfort and xe2x80x9cfeelxe2x80x9d of expensive coil spring systems, but which is less-costly to produce.
The invention provides an improved spring support system and apparatus for use in articles of furniture such as chairs and sofas, bedding, car seats or the like. The improved spring suspension system eliminates the need for the expensive eight-way hand-tied spring system and provides a resilient, cushioned surface for supporting persons seated or reclined on the surface. The improved spring support system includes a resilient sheet stretched over a plurality of springs to provide a resiliently responsive support surface suitable for use in chairs, sofas, bedding or the like. The resilient support provided by the stretchable top sheet supplements the support provided by the underlying springs, thereby reducing the number of springs (by about a third) required in a spring support system. The improved system is dynamically responsive to changes or shifts in applied loads, and provides an extremely comfortable resilient support surface. The spring support system may be integrated into an article of furniture and may be padded, covered, or upholstered to provide a finished seating or reclining surface. The spring support apparatus may also include an outer frame which is designed to be inserted into and affixed to a receiving portion of furniture frame or the like.
An apparatus according to the present invention includes an outer frame having an open bottom, an open top, a front, and a back. The front and back include opposed top edges. A lower spring support means is attached to the frame and spans the open bottom of the frame. A plurality of vertically-oriented springs are disposed in the frame. Bottom ends of the springs are affixed to the lower spring support means, and the springs are arranged in an array of rows and columns within the outer frame. A resilient top sheet is stretched (about 50%) across the open top of the frame between the opposed top edges of the front and back. The top sheet extends over the top ends of the springs, and each of the springs is at least partially vertically compressed between the lower spring support means and the top sheet, thereby preloading the springs.
Preferably, the resilient top sheet has a stretch factor of about 100. In other words, a preferred top sheet is stretchable from an unstretched width to a fully-stretched width, where the fully-stretched width is about twice as wide as the unstretched width. The top sheet is affixed to the frame such that the top sheet is stretched to about fifty percent of its fully stretched width, thereby providing a tautly stretched support surface. The top sheet may be stretched more or less on the frame depending on the desired degree of support and stiffness.
A preferred material for the top sheet is a woven or knit material comprising highly elastic yarns in the warp direction. The elastic warp yarns are formed by a resilient core wrapped by at least one substantially inelastic cover yarn. The warp yarns are interwoven with a plurality of substantially inelastic weft yarns. The woven yarns are preferably covered by a resilient outer coating such as latex which is at least partially impregnated between the interwoven yarns. This preferred material is mounted on the frame such that the top sheet is stretched in a direction which is substantially parallel to the elastic warp yarns. The cores of the warp yarns may be comprised of synthetic or natural rubber, the wrap or cover yarn is cotton, nylon, polyester, or the like, and the weft yarns are preferably polypropylene, polyester, or the like.
In a preferred arrangement, the outer frame is substantially rectangular. The lower spring support is rather conventional and preferably includes a plurality of substantially inelastic support straps which are at least partially interwoven in crossed, spaced arrangement, and extend across the open bottom of the outer frame. Ends of the straps are affixed to the frame by staples or the like. Bottom ends of the springs are affixed to the support straps at points of overlapping intersection between the interwoven straps. The lower spring support means may further include a plurality of strap reinforcement bands, wherein the reinforcement bands are affixed to the outer frame such that at least one reinforcement band underlies each of the spring support straps spanning the open bottom of the frame. Preferably, the spring support straps are constructed of woven material such as polypropylene, and the reinforcement bands are metal such as steel.
The springs are any type of resilient members which provide resilient vertical support under the top sheet. Preferably, the springs are coil springs including bottom turns. When the lower spring support means comprises interwoven straps, the bottom turns of the springs may be captured in fixed arrangement between overlapping straps. In this arrangement, a first support strap extends under the bottom turn of each spring, and a corresponding intersecting support strap extends over the bottom turn of each spring and under the first support strap. This method of attachment eliminates the need for a separate attachment means such as clips or the like between the bottom ends of the springs and the lower spring support means.
Preferably, a top turn of each coil spring is affixed to the overlying top sheet. One or more metal clips such as hog rings or the like may be used for this purpose. By affixing the top ends of the coil springs to the top sheet in this way, the springs are secured and prevented from moving laterally out of alignment in the apparatus. The clips also ensure that the springs cannot slip along the underside of the top sheet or move away from applied loads, so that loads applied to the top sheet can be effectively transmitted between adjacent springs through the top sheet.
The outer frame is preferably constructed of wood. The side edges of the sheet may be affixed to the opposed top edges of the outer frame by a plurality of staples or other suitable fasteners. The partially compressed springs may have a partially compressed spring height which is taller than the sides of the frame, such that the tautly stretched top sheet defines a substantially arcuate cover over the top ends of the springs.
The invention also includes a seat including an improved spring support system. The seat includes a frame portion comprising opposed front and rear panels and opposed end panels defining a frame interior. The front and rear panels include top and bottom edges and a first height, and the end panels have upper and lower edges and a second height, wherein the bottom edges and lower edges are substantially coplanar and define a bottom support plane. A plurality of coil springs are disposed within the frame, and include top ends and bottom ends. The springs have an uncompressed spring height which is greater than the first height of the frame side panels, and are vertically oriented in at least two rows to form a spaced array of springs within the frame interior. A lower spring support means is provided for laterally fixing and vertically supporting the bottom ends of the coil springs at points proximate the bottom support plane of the frame portion. A resilient top sheet includes opposed side edges which are affixed to the opposed top edges of the front and rear panels, respectively, such that the sheet is tautly stretched in a warp direction between the top edges and is stretched over the top ends of springs. Each of the springs is at least partially vertically compressed between the lower spring support means and the top sheet, thereby preloading the springs.
In a preferred arrangement, the seat includes a frame portion which is substantially rectangular. As described above, the spring support means may include a plurality of spring support straps which are interwoven in spaced arrangement and tautly stretched across the bottom of the frame portion. The coil springs may be affixed to the support straps at points of overlapping intersection of the interwoven straps. Reinforcement bands may be provided under the support straps to provide additional support under the springs. Bottom turns of the springs may be engaged on the interwoven straps to secure the springs in place, and top turns of the coils are preferably attached to the top sheet by a series of metal clips. The top sheet is preferably constructed of a highly-stretchable, woven elastic material as summarized above.